Transcript Cosmological Transient Objects

Cosmological Transient Objects
Poonam Chandra
Royal Military College of Canada
Raman Research Institute
14th December 2010
Cosmological Transient Objects
Supernovae
and
Gamma Ray Bursts
Supernovae and Gamma Ray Bursts
• Supernova energy 1029 more than an
atmospheric nuclear bomb explosion.
• At the time of explosion, the supernova can
shine brighter than the host galaxy consisting
of billions of stars.
• In one month, a supernova can emit as much
energy as Sun would emit in its entire life span
of billions of years.
• GRBs: biggest source of gamma-rays in
universe and 100 times more energetic than
supernovae.
Outline (Gamma Ray Bursts)
• Challenges
• How to meet the challenge: multiwaveband
modeling
• Importance of radio observations
• Our radio campaign and some results
• Future of gamma ray burst science
Gamma Ray Bursts
• A big challenge when discovered in 1960s.
• Gamma-ray signals for just a fraction of
seconds to at most few minutes.
• Non-terrestrial origin
• BATSE: isotropic
Meszaros and Rees 1997
Major breakthrough
• BeppoSAX: first detection of X-ray counterpart
of GRB 970228.
• Optical detection after 20 hours.
GRB 970508: a watershed event
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X-ray BeppoSAX
Optical , z=0.835 => Cosmological
Scintillation: fireball model
Radio, late time- energetics
• GRB 980425/SN1998bw- massive star origin
Crisis: GRB 990123
• Assuming isotropy, the g-ray energies
spanned three orders of magnitude: 3×1051 to
3×1054 erg
• Central engine energy requirements??
The GRB Energy Crisis circa 1999
ApJ 519, L7, 1999
Piran, Science, 08 Feb 2002
Stan Woosley says “I’m a
very troubled theorist.”
M sun  c 2  2 1054 erg
Astrophysics at the Extremes, Dec. 1517, 2009, Hebrew University
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Jet Signatures
tjet
Flux Density
t
t -1/3
1/2
t -2
t -1
tj
time
Harrison et al. 1999
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The GRB Energy Crisis Resolved
Frail et al (2001)
That was then…
The GRB energy crisis was resolved
GRB outflows are highly beamed (θ ~ 1-10 degrees)
Geometry measured from jet break signature in light curves
Beaming-corrected radiated energies are narrowly distributed
around a “standard” value of ~1051 erg
• A host of other measurements (X-ray afterglows, broadband
modeling, calorimetry) support this energy scale
• This energy scale is consistent with models of GRB central
engines
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This is now… POST-SWIFT
1. The mystery of the missing jets in the Swift era.
2. The emerging population of hyper-energetic events.
3. The established class of sub-energetic gamma-ray bursts.
Multiwaveband modeling
• Long lived
afterglow with
powerlaw decays
• Spectrum broadly
consistent with the
synchrotron.
• Measure Fm, nm, na,
nc and obtain Ek
(Kinetic energy), n
(density), ee, eb
(micro parameters),
theta (jet break), p
(electron spectral
index).
Radio Observations
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Late time follow up- accurate calorimetry
Scintillation- constraint on size
VLBI- fireball expansion
Density structure- wind-type versus constant
Multiwaveband modeling
Radio afterglow statistics: 1997-2010
•1/3rd of all GRBs
seen as radio
afterglows since
1997-2010.
•93 out of 244
•46 out of 149 (post
Swift)
•No strong redshift
dependence.
•z<2 47/88
• z>2 21/43
Chandra et al. 2011
Radio afterglow statistics: post-Swift
•1/3rd of all GRBs
seen as radio
afterglows since
1997-2010.
•93 out of 244
•46 out of 149 (post
Swift)
•No strong redshift
dependence.
•z<2 47/88
• z>2 21/43
Chandra et al. 2011
Radio spectral luminosity at 8.5 GHz (erg/s/Hz)
Canonical radio afterglow light curve
1e+32
1e+31
1e+30
1e+29
980425
030329
060218
070125
090423
1e+28
1e+27
1e+26
0.1
1
10
Days since bursts
100
1000
GRB 070125 (Chandra et al. 2008)
• One of the brightest Swift burst with isotropic
energy of 1.1x1054 erg.
• Followed extensively in X-ray, optical, mm and
radio bands.
• In radio bands, observed for more than a year.
GRB 070125: Scintillation
(Chandra et al. 2008)
Jet break in GRB 070125
Chandra et al. 2008
• Chromatic jet
break…
• Optical band, day 3
• X-ray band, day 10
• Explanation—
– Inverse-Compton
Mechanism
Inverse-Compton in X-rays
Inverse Compton Scattering
• Possible explanation for the delay in jet breaks
or chromatic jet breaks in various GRBs.
• Does not affect radio and optical bands but
dominates in X-ray bands.
• More effective in high-density environments.
Radio data is crucial.
GRB 070125: Highlights (Chandra et al. 2008)
• Diffractive scintillation- constrain the fireball
size
• Chromatic jet break- Inverse Compton
• Collimated g-energy 2.5x1052 erg.
• Kinetic energy 1.7x1051 erg.
GRB 090423
• Highest redshift GRB at z=8.2
• Highest redshift object of any kind known in
our Universe.
• Must have exploded just 630 million years
after the Big Bang.
GRB 090423
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X-ray observtions: 73 s after detection
Optical observations: 109 s after detection
No optical transient.
Detection in J band onwards.
Photo-z=8.06+/-0.25
Spectral-z=8.23+/-0.08
Radio observations of GRB 090423
(Chandra et al. 2010)
Detections VLA: 8.5 GHz on Apr 25-Jun
27.
– 74 +/- 22 uJy at Δt~8 d
– 2-hr integrations every 2
days
– Data sets averaged (in UV
plane) to improve
detection sensitivity
– Undetectable after Δt~65 d
PdBI: 95 GHz on Apr 23-24
– Castro-Tirado et al.
report a secure source
detection of 200 uJy (no
error bar given)
Non-Detections WSRT: 4.9 GHz on May 22-23
CARMA: 95 GHz on Apr. 25
IRAM 30-m: 250 GHz on Apr
25
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Multiwaveband modeling:
(Chandra et al. 2010)
Broadband modeling
• High energy burst exploded in constant
density medium.
• No jet break occurred until day 50.
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Reverse shock emission in GRB 090423
• Reverse shock emission at day 9 (time dilated)
• After 1+z correction, reverse shock on day 1
• Seen is 250 GHz data also at around 10 hours
(1+z corrected).
• Implications for high Lorentz factor
Previous high redshift GRB 050904 z=6.26
Afterglow Properties –
– GRB 050904 (z=6.26). Both are hyper-energetic
(>1051 erg) but they exploded in very different
environments. (in situ n=600 cm-3 for GRB
050904)
– Large energy predicted for Pop III. Not unique.
– Low, constant density predicted for Pop III. Not
unique.
– No predictions for θj, εB, εe & p
– Reverse shock detection in both GRBs
Radio spectral luminosity at 8.5 GHz (erg/s/Hz)
Canonical radio afterglow light curve
1e+32
1e+31
1e+30
1e+29
980425
030329
060218
070125
090423
1e+28
1e+27
1e+26
0.1
1
10
Days since bursts
100
1000
Reverse shock in radio GRBs
Chandra et al. 2010b
• Swift had expected to find
many RS
• At most, 1:25 optical AG have
RS
• Favored explanation
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Ejecta are magnetized (i.e. σ>1).
Do not need to be fully Poynting-flux
dominated
Suppresses RS emission
Kulkarni et al. (1999)
• Does not explain why prompt
radio emission is seen more
frequently.
• About 1:4 radio AG may be
RS
• Possible Explanation: The RS
spectral peak is shifted out of
the optical band to lower
frequencies
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A seismic shift in radio afterglow
studies
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The VLA got a makeover!
More bandwidth, better receivers, frequency coverage
20-fold increase in sensitivity
Capabilities started in 2010
• GRBs at higher frequencies where ISS is reduced
• Measure polarization and rotation measures
• Absorption lines possible (CO; see Inoue et al. 2007)
Future of GRB Physics
• Expanded Very Large Array (EVLA)
• 20 times more sensitive than the VLA.
Future: The EVLA- accurate
calorimetry
EVLA, 3-s, z=8.5 1 hr
EVLA, 3-s, z=2.5 1 hr
Future: Atacama Large Millimeter
Array (ALMA)
Accurate determination of
kinetic energy
Future: ALMA
Debate between wind versus ISM solved
Future: ALMA
Reverse Shock at high redshifts
mm emission from RS is bright, redshiftindependent (no extinction or scintillation)
(Inoue et al. 2007). ALMA will be ideal.
Conclusions
• Multiwaveband modeling required to understand the
GRB afterglow Physics.
• New class of hyperenergetic GRBs such as GRB 070125.
• Star formation taking place even at 630 million years
after the big bang.
• New explanation for the delay in jet breaks in Swift
bursts
• Radio and mm is crucial as they are unique in
estimating the accurate energy, density and type of
medium.
• Future lies with the EVLA and the ALMA.
Supernovae
• Chandra, Dwarkadas, et at. 2009, ApJ 699, 388
– X-rays from the explosion site: 15 years of light curves of SN
1993J.
• Nymark, Chandra, Fransson 2009, A &A 494, 179
– Modeling the X-ray emission of SN 1993J.
• Patat, Chandra, et al. 2007, Science 317, 924
– Detection of circumstellar material in a normal Type Ia supernova.
• Chandra, Ray, et al. 2005, ApJ 629, 933
– Chandra’s tryst with SN 1995N.
• Chandra, Ray, Bhatnagar 2004, ApJ 612, 974
– The late time radio emission from SN 1993J at meter wavelengths.
• Chandra, Ray, Bhatnagar 2004, ApJL 604, 97
– Synchrotron aging and radio spectrum of SN 1993J.
Collaborators for GRB work
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Dale Frail
Shri Kulkarni
Brad Cenko
Derek Fox
Edo Berger
Fiona Harrison
Mansi Kasliwal
THANKS